Technical Field
The present invention relates to a composite and a method of manufacturing a composite epoxy material with embedded multi walled carbon nanotube (MWCNT) fibers.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Polymer based composites reinforced with a small percentage of strong fillers were shown to significantly improve the thermal, mechanical and barrier properties of the pure polymer matrix. See N. Chisholm, H. Mahfuz, V. K. Rangari, A. Ashfaq, S. Jeelani: Fabrication and mechanical characterization of carbon/SiC epoxy nanocomposites, Composite Structures 67 (2005), pp. 115-124, incorporated herein by reference in its entirety. Moreover, improvements on the thermal, mechanical, and barrier properties were achieved through conventional processing techniques without any detrimental effects on appearance, processing, density and ageing performance of the matrix. Eventually, these composites were considered for a wide range of applications including coating, packaging, electronics, automotive and aerospace industries. While nanoparticles have attractive attributes, they are rarely used in structural composites which have relatively large dimensions. Recently, nanofillers, such as multi walled carbon nanotubes (MWCNT), carbon nanofibers, pyrogenic silica, nanoclay, polyhedral oligomeric silsequioxane, and diatomites, were used by researchers to modify different types of epoxy resin to enhance desired attributes. See K. Tao, S. Yang, J. C. Grunlan, Y. S. Kim; B. Dang, Y. Deng, R. L. Thomas, B. L. Wilson, X. Wei: Effects of Carbon Nanotube Fillers on the Curing Processes of Epoxy Resin-Based Composites, J. Applied Polymer Science 102 (2006), pp. 5248-5254; M. A. Megahed, A. A. Megahed, H. E. M. Sallam, U. A. Khashaba, M. A. Seif, M. Abd Elhamid: Nano-Reinforcement Effects on Tensile Properties of Epoxy Resin, Proc. of the int. Conf. MEATIP5, Assiut University, Egypt (2011), pp. 123-135; X. Zhou, E. Shin, K. W. Wang, C. E. Bakis: Interfacial damping characteristics of carbon nanotube-based composites, Composites Science and Technology 64 (2004), pp. 2425-21437; S. Bal: Experimental study of mechanical and electrical properties of carbon nanofiber/epoxy composites, Materials and Design 31 (2010), pp. 2406-2413; N. Hu, Y. Li, T. Nakamura, T. Katsumata, T. Koshikawa, M. Arai: Reinforcement effects of MWCNT and VGCF in bulk composites and interlayer of CFRP laminates, Composites Part B 43 (2012), pp. 3-9; S. U. Khan, C. Y. Li, N. A. Siddiqui, J. K. Kim: Vibration damping characteristics of carbon fiber-reinforced composites containing multi walled carbon nanotubes, Composites Science and Technology 71 (2011), pp. 1486-149; Zhou, F. Pervin, S. Jeelani, P. K. Mallick: Improvement in mechanical properties of carbon fabric-epoxy composite using carbon nanofibers, J. Materials Processing Technology 198 (2008); pp. 445-453; P. R. Mantena, A. Al-Ostaz, A. H. D. Cheng: Dynamic response and simulations of nanoparticle-enhanced composites, Composites Science and Technology 69 (2009), pp. 772-779; M. R. Ayatollahi, S. Shadlou, M. M. Shokrieh: Fracture toughness of epoxy/multi-walled carbon nanotube nano-composites under bending and shear loading conditions, Materials and Design 32 (2011), pp. 2115-2124; L. Sun, G. L. Warren, J. Y. O'Reilly, W. N. Everett, S. M. Lee, D. Davis, D. Lagoudas, H. J. Sue: Mechanical properties of surface-functionalized SWCNT/epoxy composites, Carbon (2008), pp. 320-328; R. F. Gibson, E O. Ayorinde, Y. F. Wen: Vibrations of carbon nanotubes and their composites: A review, Composites Science and Technology 67 (2007), pp. 1-28; D. Qian, C. Dickey, R. Andrews, T. Rantell: Load transfer and deformation mechanism in carbon nanotube-polystyrene composites, Appl. Phys. Lett. 76 (2000), No. 20, pp. 2868-2870; C. Velasco-Santos, A. L. Martinez-Hernandez, F. Fisher, R. Ruoff, V. M. Castano: Dynamic mechanical and thermal analysis of carbon nanotube-methylethylmethacrylate nanocomposites, J. Phys. D. 36 (01/2003), pp. 1423-1428; Z. L. Jin, S. J. Park: Thermal properties of epoxy resin/filler hybrid composites, Polymer Degradation and Stability 97 (2012), pp. 2148-2153; W. Jiang, F. L. Jin, S. J. Park: Thermo-mechanical behaviors of epoxy resins reinforced with nano-Al2O3 particles, Journal of Industrial and Engineering Chemistry 18 (2012), pp. 594-596; M. S. Goyat, S. Ray, P. K. Ghosh: Innovative application of ultrasonic mixing to produce homogeneously mixed nanoparticulate-epoxy composite of improved physical properties, Composites Part A 42 (2011), pp. 1421-1431; O. Akinyede, R. Mohan, A. Kelkar, J. Sankar: Static and fatigue behavior of epoxy/fiberglass composites hybridized with alumina nanoparticles, J. Composite Materials 43 (2009), pp. 769-781; H. Zhao, R. K. Y. Li: Effect of water absorption on the mechanical and dielectric properties of nano-alumina filled epoxy nanocomposites, Composites Part A 39 (2008), pp. 602-611; C. Ocando, A. Tercjak, I. Mondragon: Nanostructured systems based on SBS epoxidized triblock copolymers and weildispersed alumina/epoxy matrix composites, Composites Science and Technology 70 (2010), pp. 1106-1112; S. H. Lim, K. Y. Zeng, C. B. He: Morphology, tensile and fracture characteristics of epoxyalumina nanocomposites, Materials Science and Engineering A 527 (2010), pp. 5670-5676; D. K. Shukla, S. V. Kasisomayajula, V. Parameswaran: Epoxy composites using functionalized alumina platelets as reinforcements, Composites Science and Technology 68 (2008), pp. 3055-3063; M. F. Uddin, C. T. Sun: Improved dispersion and mechanical properties of hybrid nanocomposites, Composites Science and Technology 70 (2010), pp. 223-230, each incorporated herein by reference in its entirety.
Significant effort has been focused on improving epoxy materials using nanofillers such as TiO2, SiC, silver, SiO2, Al2O3, and carbon nanotubes (CNT). See B. Bittmann, F. Haupert, A. K, Schlarb: Ultrasonic dispersion of inorganic nanoparticles in epoxy resin, Ultrasonics Sonochemistry 16 (2009), pp. 622-628; D. I. Tee, M. Mariatti, A. Azizan, C. H. See, K. F. Chong: Effect of silane-based coupling agent on the properties of silver nanoparticles filled epoxy composites, Composites Science and Technology 67 (2007), pp. 2584-2591; C. Chen, R. S. Justice, D. W. Schaefer, J. W. Baur: Highly dispersed nanosilca epoxy resins with enhanced mechanical properties, Polymer 49 (2008), pp. 3805-3815; H. E. M. Sallam U. A. Khashaba, M. A. Seif, M. Abd-Elhamid, A. A. Megalied, M. A. Megahed: Ultrasonic mixing of nanoparticles in epoxy resin, Proc, of the Int. Conf, on Nano Technology for Green and Sustainable Construction, Cairo, Egypt (2010), pp. 312-316; N. Lachman, H. D. Wagner: Correlation between interfacial molecular structure and mechanics in CNT/epoxy nano-composites, Composites Part A 41 (2010), pp. 1093-1098; S. Ganguli, H. Aglan, P. Dennig, G. Irvin: Effect of loading and surface modification of MWCNTs on the fracture behavior of epoxy nanocomposites, Journal of Reinforced Plastics and Composites (2006), pp. 175-188; J. P. Yang, Z. K. Chen, Q. P. Feng, Y. H. Deng, Y. Li, Q. Q. Ni, S. Y. Yu: Cryogenic mechanical behaviors of carbon nariotube reinforced composites based on modified epoxy by poly(ethersulfone), Composites Part B 43 (2012), pp. 22-26; F. Mujika, G. Vargas, J. Ibarretxe, J. De Gracia, A. Arrese: Influence of the modification with MWCNT on the interlaminar fracture properties of long carbon fiber composites, Composites Part B 43 (2012), pp. 1336-1340; V. K. Srivastava: Modeling and mechanical performance of carbon nanotube/epoxy resin composites, Materials and Design 39 (2012), pp. 432-436; M. R. Loos, J. Yang, D. L. Feke, I. Manas-Zloczower: Effect of block-copolymer dispersants on properties of carbon nanotube/epoxy systems, Composites Science and Technology, 72 (2012), pp. 482-488, each incorporated herein in its entirety. CNT have taken a prominent position for a new generation of high-performance nanocomposites because of their novel structure and several remarkable mechanical, thermal and electrical properties. See H. C. Kim, S. K. Kim, J. T. Kim, K. Y, Rhee, J. Kathi: The Effect of Different Treatment Methods of Multiwalled Carbon Nanotubes on Thermal and Flexural Properties of Their Epoxy Nanocomposites, J. Polymer Science Part Polymer Physics 48 (2010), pp. 1175-1184, incorporated herein by reference in its entirety. CNT are known to have a plastic modulus of up to 1 TPa and predictable tensile strengths in the range of 100 GPa. In combination with these properties, CNT also have unusually low density for lightweight structures. Because of their ultra-small, nanometer scale size and low density, the surface area to mass ratio (specific area) of carbon nanotubes is extremely large. Therefore, a nanotube-based polymeric composite structure can achieve high damping by taking advantage of the interfacial friction between the nanotubes and the polymer resins. In addition, the CNT large aspect ratio and high elastic modulus features allow for the design of such composites with large differences in strain between the constituents, which could further enhance the interfacial energy dissipation ability. See R. M. Lin, C. Lub: Modeling of interfacial friction damping of carbon nanotube-based nanocomposites, Mechanical Systems and Signal Processing 24 (2010), pp. 2996-3012, incorporated herein by reference in its entirety. Accordingly, CNT-based composites are becoming increasingly popular and offer great potential for highly demanding damping applications such as aerospace structures, precision engineering, micro-positioning and control.
The outstanding properties of carbon nanotubes make them promising filler material to improve mechanical, thermal and electrical properties of polymers. The key point is to transfer the potential properties of CNT to the polymer composites. Due to the high-surface energy, nanofillers have a tendency to aggregate together owing to the strong attractive forces. The van der Waals attractive interactions owing to high aspect ratio of nanofillers are another reason for their agglomeration in epoxy resins. The aggregated CNT are in the form of bundles or ropes, usually with highly entangled network structure so that is very difficult to disperse them. See M. Tanahashi: Development of fabrication methods of filler/polymer nanocomposites: With focus on simple melt-compounding-based approach without surface modification of nanofillers, Materials 3 (2010), pp. 1593-1619; A. Montazeri, N. Montazeri: Viscoelastic and mechanical properties of multiwalled carbon nanotube/epoxy composites with different nanotube content, Materials and Design 32 (2011), pp. 2301-2307; S. Yang, W. Lin, Y. Huang, H. Tien, J. Wang, C. M. Ma, S. Li, Y. Wang: Synergetic effects of graphene platelets and carbon nanotubes on the mechanical and thermal properties of epoxy composites, Carbon 49 (2011), pp. 793-803; M. Theodore, M. Hosur, J. Thomas, S. Jeelani: Influence of functionalization on properties of MWCNT-epoxy nanocomposites, Materials Science and Engineering A 528 (2011), pp. 1192-1200; A. Martone, C. Formicola, M. Giordano, M. Zarrelli: Reinforcement efficiency of multiwalled carbon nanotube/epoxy nanocomposites. Composites Science and Technology 70 (2010), pp. 1154-1160, each incorporated herein by reference in its entirety. The homogeneous dispersion of nanofillers within the polymer matrix is a prerequisite of any composites and remains a problem to be solved.
Different techniques have been used to enhance the dispersion of nanofillers in polymer resins, including the use of melt mixing, mechanical shear mixer, sol-gel (modification of the chemical surface of fillers), in situ polymerization, three-roll mill, ball milling and mechanical stirring. According to previous researchers, ultrasonic agitation method is more effective to disperse CNT in epoxy resins. See J. S. Tang, J. Varischetti, G. W. Lee, J. Suhr: Experimental and analytical investigation of mechanical damping and CTE of both SiO2 particle and carbon nanofiber reinforced hybrid epoxy composites, Composites Part A 42 (2011), pp. 98-103; A. Martone, C. Formicola, F. Piscitelli, M. Lavorgna, M. Zarrelli, V. Antonucci, M. Giordano: Thermo-mechanical characterization of epoxy nanocomposites with different carbon nanotube distributions obtained by solvent aided and direct mixing, J. Express Polymer Letters 6 (2012), pp. 520-531, each incorporated herein in its entirety. Currently, high power ultrasonic liquid processors are used to disperse MWCNTs in epoxy resin.
In sonication, the sonication probe generates high-intensity ultrasound waves that penetrate into the liquid filler matrix mixture, where cavitation bubbles can develop and grow during several cycles until they attain a critical diameter, which induces their implosion. This collapse causes extreme local conditions as a very high local pressure and very high temperatures, a so called hot-spot. Due to these hot-spots a splitting up of filler agglomerates can occur. The shock waves from the implosive bubble collapse in combination with micro-streaming generated by cavitation oscillations lead to dispersion effects. If a mixture contains a gas like air, more bubbles will be likely formed during sonication, which can lead to a better dispersion. On the other hand, the entrapped air impairs the flow ability of the mixture. Thus, a positive effect superimposes a negative effect. Sonication parameters can play an important role in enhancement of the dispersion of nanofillers in viscous polymers. These parameters are: sonication power, frequency, amplitude, time, temperature, energy, energy density, dimensions of sonication probe, immersion depth of the sonication probe, and sonication mode (pulsed or continuous), See J. L. Tsai, M. D. Wu: Organoclay effect on mechanical responses of glass/epoxy nanocomposites, Compos. Mater. 6 (2008), pp. 553-568, incorporated herein in its entirety.
The literature on ultrasonic dispersion of nanoparticles in epoxy resin presents varying processing parameters to achieve the dispersion of nanoparticles in epoxy resin. Wide varieties of sonication power were observed by a number of investigators for dispersing nanofillers in epoxy resin: 350 W, 500 W, 600 W, and 750 W. Bittmann et al. found that the dispersion of titanium dioxide nanoparticles in epoxy resin at highest sonication of 100%, and hence the highest power input, leads to the best dispersion result. See S. Zhao, L. S. Schadler, R. Duncan, H. Hillborg, T. Auletta: Mechanisms leading to improved mechanical performance in nanoscale alumina filled epoxy, Composites Science and Technology 68 (2008), pp. 2965-2975, incorporated herein in its entirety. Sonicator probe diameter can play an important role in dispersion of nanofillers in epoxy resin. Most of the supplied probes with the ultrasonic processors have diameters of about 12.5 mm or 25 mm. See O. Asi: Mechanical properties of glass-fiber reinforced epoxy composites filled with Al2O3 particles, J. Reinforced Plastics and Composites 28 (2009), pp. 2861-2867, herein incorporated in its entirety. Larger sonication probe diameters produce less intensity, but the energy is released over a greater area and accordingly, larger volume can be processed. Therefore, a sonication probe diameter must be considered carefully based on the specific goals of the project.
Sonication in pulsed mode retards the rate of temperature increase in a mixture of epoxy resin and nanoparticles, minimizing unwanted side effects and allowing better temperature control than continuous mode operation. Different pulsing mode intervals were observed by many researchers: 15 s on and 59 s off, 12 s on and 48 s off, 5 s on and 9 s off, 15 s on and 15 s off, and 50 s on and 25 s off. Pulse mode operation with long off periods will help to avoid foaming in samples.
Some researchers studied the viscoelastic and mechanical properties of MWCNT/epoxy composites with different weight fractions by performing tensile and dynamic mechanical thermal analysis (DMTA) tests. The MWCNT/epoxy nanocomposites were fabricated by sonication and a cast molding process. The results showed that the tensile strength and modulus for 2 wt.-% MWCNT increased by 17% and 23%, respectively. Compared to neat epoxy, the dynamic mechanical results indicated a 46% improvement in storage modulus for 0.5 wt.-% MWCNT/epoxy at room temperature.
The influence of alumina nanoparticles and MWCNT in monolithic and hybrid forms on the mechanical properties of nanocomposites was investigated by one study. See A. Alva, A. Raja: Dynamic characteristics of epoxy hybrid nanocomposites, Journal of Reinforced Plastics and Composites 30 (2011), pp. 1857-1867, incorporated herein in its entirety. In the study, the MWCNT were mixed with epoxy resin by manual stirring for 20 min. The results showed that the storage moduli (Young's modulus) of the alumina nanocomposites with 0.5 and 1.0 wt.-% nano-alumina loading, improved by 15.0% and 7.4%, respectively, which are higher than obtained for MWCNT nanocomposites. The authors attributed the lower improvement in the storage moduli of MWCNT nanocomposites to the poor dispersion of MWCNT. Hence, the authors recommended using alternative dispersion techniques such as ultrasonication or a three-roll mixer to minimize the agglomerations of MWCNT in epoxy.
Epoxy monomers react with curing agent during curing to form a three-dimensional cross-linked network with certain thermomechanical properties. The degree and uniformity of curing reaction will affect considerably the bulk material properties. See R. M. Rodgers, H. Mahfuz, V. K. Rangari, S. Jeelani, L. Carlsson: Tensile response of SiC nanoparticles reinforced epoxy composites at room and elevated temperatures, Proc. of the 16th Int. Conf. Composite Materials, Kyoto Japan (2007), pp. 1-6 48; L E. Sawi, P. A. Oiivier, P. Demont, H. Bougherara: Investigation of the effect of double-walled carbon nanotubes on the curing reaction kinetics and shear flow of an epoxy resin, Journal of Applied Polymer Science 126 (2012), pp. 358-366, each incorporated herein in its entirety. Various degrees of nanofiller concentrations may influence curing reactions to a different degree or sometimes with opposite effect. See J. P. Pascault, R. J. J. Williams: Epoxy Polymers New Materials and Innovations, Wiley-VCH Verlag, Weinheim, Germany (2010); M. Preghenella, A. Pegoretti, C. Migliaresi: Thermo-mechanical characterization of fumed silica-epoxy nanocomposites, Polymer 46 (2005), pp. 12065-12072 each incorporated herein in its entirety. Studies showed that both unfunctionalized and functionalized MWCNT have an accelerating influence on the reaction kinetics. Zhou et al. also found that the degree of epoxy cure is decreased by the addition of 1 wt.-% unfunctionlized MWCNT. This result was evidenced by the lower value of the glass transition temperature (Tg) of the cured nanocomposite by 15° C. compared to the neat epoxy. Tao et al. also observed that with only 1 wt.-% of carbon nanotubes, the Tg of epoxy composites was lowered by approximately 10-30° C.
The weight and fuel savings offered by composite materials make them attractive not only to the military, but also to the civilian aircraft, space, and automobile industries. In these industries, bolted and riveted joints are extensively used as a primary method for structural joining. Bolted joints in composite materials have complex failure modes, and hence the demand for improving their performance exists.
In view of the forgoing, the objective of the present invention is to improve the tensile and compressive strength and strain performance of a stacked composite material prepared with glass fiber and a nanocomposite of epoxy resin and MWCNT.